Question

When chromite ore $Fe{Cr}_2{O}_4$ is fused with $NaOH$ in presence of air, a yellow coloured compound (A) is obtained which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with $KCl$ forms a orange coloured crystalline compound (C).
(i) Write the formulae of the compounds (A), (B), and (C).
(ii) Write one use of compound (C).
OR
Complete the following chemical equations:
(i) $8Mn{O}_4^{-}+3S_2{O}_3^{2-}+H_{2}O\to$
(ii) ${Cr}_2{O}_7^{2-}+3{Sn}^{2+}+14H^{+}\to$

Answer 1

When chromite ore $FeC{r}_2{O}_4$ is fused with $NaOH$ in presence of air, a yellow coloured compound obtained is chromate $N{a}_{2}Cr{O}_4$ (A).

$FeC{r}_2{O}_4+NaOH+O_2\to N{a}_{2}Cr{O}_4+F{e}_2{O}_3+H_{2}O$

This chromate with acidification with $H_{2}S{O}_4$ forms sodium dichromate (B), sodium sulfate and water.

$N{a}_{2}Cr{O}_4+H_{2}S{O}_4\to N{a}_{2}C{r}_2{O}_7+N{a}_{2}S{O}_4+H_{2}O$

Sodium dichromate with $KCl$ forms an orange crystalline compound potassium dichromate (C) .

$N{a}_{2}C{r}_2{O}_7+KCl\to K_{2}C{r}_2{O}_7+NaCl$

Or

$\left(i\right)8{MN{O}_4}^{-}+3S_2{O}_3^{2-}+H_{2}O\to 8MN{O}_2+6S{O}_4^{2-}+2O{H}^{-}$

$\left(ii\right)C{r}_2{O}_7^{2-}+3S{n}^{2+}+14H^{+}\to 2C{r}^{3+}+3S{n}^{4+}+6H_{2}O$